The information in this document is based on the CSS 11150 SW Version:
6.10 Build 107.

The information in this document was created from the devices in a
specific lab environment. All of the devices used in this document started with
a cleared (default) configuration. If your network is live, make sure that you
understand the potential impact of any command.

CSSs participate in a redundant configuration when a redundancy link
has been defined between two CSSs. The protocol used for this redundancy link
is VRRP, using multicast address 224.0.0.18. The CSSs use this link to maintain
contact and activity status with one another. Only one crossover link between
the CSSs is supported. You must use a crossover cable to connect directly to
the FE ports on the redundant CSSs. Do not use Layer 2 devices between the two
CSSs on the redundant link. Do not install the crossover cable on Gigabit
Ethernet (GE) ports; this configuration is not supported.

Note: The CSS box-to-box redundancy protocol is now supported on the CSS
11501, CSS 11503, and CSS 11506 GE ports in software version 7.10.1.02 and
7.20.0.01 and later.

There are two main conditions detected on this redundancy link that
drive master and backup states on the two CSSs:

The first condition is maintaining the heartbeat, which is an
advertisement every second. The master CSS provides this heartbeat on the
redundancy link, and the backup CSS keeps track of the heartbeat every three
seconds (default). If the heartbeat times out (for example, heartbeats are not
detected in this period), then the backup takes over as master.

The new master CSS begins sending out redundancy protocol messages as
well as gratuitous Address Resolution Protocol (ARP) messages to update the ARP
tables on neighboring nodes and the forwarding tables of attached bridging
devices (for example, Layer 2 switches) with the new master CSS MAC address.
The CSS transmits one ARP request packet and one ARP reply packet for every
gratuitous ARP invocation.

The second condition is that of a VRRP switch priority change. The
CSS advertising the highest priority is negotiated to become master. This is
the mechanism used by the uplink services, and some of the special commands
(described below) for initiating a failover event.

Note that in the event that the CSSs are misconfigured (for example,
two or more CSSs are set up as the IP redundancy master), the CSS with the
highest VRRP IP address takes over as the master.

In this section, you are presented with the information to configure
the features described in this document.

Issue the ip redundancy command to enable
CSS-to-CSS redundancy on two CSSs interfaced with a crossover cable. By
default, redundancy is disabled on the CSSs until you issue this command on
both CSSs.

When you include the master option with this
command, you can designate which CSS is the master CSS. Initially, booting two
CSSs interfaced with a crossover cable determines which is the master and which
is the backup. The CSS that boots first is the master CSS. If the CSSs boot at
the same time, the CSS with the numerically higher IP address becomes the
master.

When you issue the ip redundancy master
command on the CSS, the CSS becomes the master CSS. You can issue this command
on either the current master or backup. If you issue the
master option on the backup CSS, the CSS becomes the
master and the other CSS automatically becomes the backup.

If you designate a master CSS, the CSS regains master status after
going down and then comes up again. For example, when the master CSS goes down,
the backup CSS becomes master. When the former designated master CSS comes up
again, however, the CSS becomes the master again.

If you have no requirement to designate a CSS as the master when both
CSSs are up, do not include the master option when
enabling redundancy on the master CSS.

You can create a service that is associated with a router’s IP address.
This service enables the master CSS to monitor the router with a keepalive
(ICMP). If the keepalive fails, the master relinquishes control and the backup
CSS takes control. You can configure more than one service by issuing the
type redundancy-up command; the CSSs use all
redundancy uplinks when making the failover decision.

If a CSS is active, and loses all uplinks designated as redundancy-up,
the CSS relinquishes the active state and becomes the backup. The CSS uses the
redundancy protocol to inform the other CSS to become active. If both CSSs have
lost their uplinks, a CSS stays in the active state for 45 seconds, waiting for
the uplink to come alive. After 45 seconds, if there is still no viable uplink,
the CSS goes into backup mode, giving the other switch a try. This allows both
CSSs to get a chance to test their uplinks without thrashing back and forth
many times each minute.

Note: A CSS goes into failover when there are no longer live uplink
services.

This feature is disabled when the ip redundancy
master command is issued. When the ip redundancy
master command is issued, the type
redundancy-up command cannot be configured. When a service is
configured by issuing the type redundancy-up
command, the ip redundancy master command cannot be
issued.

If any one of the physical interfaces configured for redundancy goes
down, the CSS relinquishes control, and the backup CSS immediately takes over
as master. This feature is based on link state as opposed to the redundancy-up
service, which is based on IP connectivity. The CSS can determine link state
when in backup mode. You must make sure that the upstream or downstream path of
the backup CSS does not also run through this same interface; this will cause
the CSS boxes to flap the ownership of the master status.

This feature is disabled by issuing the ip redundancy
master command. When the ip redundancy
master command is issued, the redundancy-phy
interface command fails. When the
redundancy-phy interface
command is issued, the ip redundancy master command
fails.

sh redundancy— This command verifies that
the CSSs are running in a redundant configuration; this command also displays
which CSS is master and which is backup, as well as the reason for the last
failover.

You can force the backup to master for maintenance purposes. Issue the
redundancy force-master command to configure a
backup CSS as a temporary master. This is a temporary setting because the
command is not copied to the running-configuration. This command is useful in a
redundant configuration when you need to take the master CSS offline for
maintenance or an upgrade.